On Fri, 2020-12-04 at 01:18 +0000, David Woodhouse wrote: > Reviving the first section (so far) of a patch set that Joao posted as > RFC last year: > > https://lore.kernel.org/kvm/20190220201609.28290-1-joao.m.martins@xxxxxxxxxx/ > > This adds basic hypercall interception support, and adds support for > timekeeping and runstate-related shared info regions. > > I've updated and reworked the original a bit, including: > • Support for 32-bit guests > • 64-bit second support in wallclock > • Time counters for runnable/blocked states in runstate support > • Self-tests > • Fixed Viridian coexistence > • No new KVM_CAP_XEN_xxx, just more bits returned by KVM_CAP_XEN_HVM > > I'm about to do the event channel support, but this part stands alone > and should be sufficient to get a fully functional Xen HVM guest running. I also realise I forgot to include the RCU read-critical sections around using the pointers that might get invalidated. (This is the model I think can we use for the KVM pvclock and other pages that we currently pin too, FWIW.) That looks a bit like this. Unless there's any other useful and relevant feedback I'll post a V2 of the series over the weekend or on Monday. diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c index e49e59f93828..4aa776c1ad57 100644 --- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -86,19 +86,21 @@ static void *xen_vcpu_info(struct kvm_vcpu *v) { struct kvm_vcpu_xen *vcpu_xen = vcpu_to_xen_vcpu(v); struct kvm_xen *kvm = &v->kvm->arch.xen; - unsigned int offset = 0; - void *hva = NULL; + void *hva; - if (vcpu_xen->vcpu_info) - return vcpu_xen->vcpu_info; + hva = READ_ONCE(vcpu_xen->vcpu_info); + if (hva) + return hva; - if (kvm->shinfo && v->vcpu_id < MAX_VIRT_CPUS) { - hva = kvm->shinfo; - offset += offsetof(struct shared_info, vcpu_info); - offset += v->vcpu_id * sizeof(struct vcpu_info); + if (v->vcpu_id < MAX_VIRT_CPUS) + hva = READ_ONCE(kvm->shinfo); + + if (hva) { + hva += offsetof(struct shared_info, vcpu_info); + hva += v->vcpu_id * sizeof(struct vcpu_info); } - return hva + offset; + return hva; } static void kvm_xen_update_vcpu_time(struct kvm_vcpu *v, @@ -139,6 +141,7 @@ static void kvm_xen_update_runstate(struct kvm_vcpu *vcpu, int state, u64 steal_ struct compat_vcpu_runstate_info *runstate; u32 *runstate_state; u64 now, delta; + int idx; BUILD_BUG_ON(sizeof(struct compat_vcpu_runstate_info) != 0x2c); BUILD_BUG_ON(offsetof(struct vcpu_runstate_info, state) != @@ -146,7 +149,8 @@ static void kvm_xen_update_runstate(struct kvm_vcpu *vcpu, int state, u64 steal_ BUILD_BUG_ON(sizeof(((struct vcpu_runstate_info *)0)->state) != sizeof(((struct compat_vcpu_runstate_info *)0)->state)); - runstate = vcpu_xen->runstate; + idx = srcu_read_lock(&vcpu->kvm->srcu); + runstate = READ_ONCE(vcpu_xen->runstate); runstate_state = &runstate->state; #ifdef CONFIG_64BIT @@ -185,6 +189,8 @@ static void kvm_xen_update_runstate(struct kvm_vcpu *vcpu, int state, u64 steal_ runstate->state_entry_time &= ~XEN_RUNSTATE_UPDATE; smp_wmb(); + + srcu_read_unlock(&vcpu->kvm->srcu, idx); } void kvm_xen_runstate_set_preempted(struct kvm_vcpu *vcpu) @@ -228,7 +234,9 @@ void kvm_xen_setup_runstate_page(struct kvm_vcpu *vcpu) void kvm_xen_setup_pvclock_page(struct kvm_vcpu *v) { struct kvm_vcpu_xen *vcpu_xen = vcpu_to_xen_vcpu(v); - struct vcpu_info *vcpu_info = xen_vcpu_info(v); + struct vcpu_info *vcpu_info; + struct pvclock_vcpu_time_info *pv_info; + int idx; BUILD_BUG_ON(offsetof(struct shared_info, vcpu_info) != 0); BUILD_BUG_ON(offsetof(struct compat_shared_info, vcpu_info) != 0); @@ -236,12 +244,17 @@ void kvm_xen_setup_pvclock_page(struct kvm_vcpu *v) BUILD_BUG_ON(offsetof(struct vcpu_info, time) != offsetof(struct compat_vcpu_info, time)); + idx = srcu_read_lock(&v->kvm->srcu); + vcpu_info = xen_vcpu_info(v); if (likely(vcpu_info)) kvm_xen_update_vcpu_time(v, &vcpu_info->time); /* Update secondary pvclock region if registered */ - if (vcpu_xen->pv_time) - kvm_xen_update_vcpu_time(v, vcpu_xen->pv_time); + pv_info = READ_ONCE(vcpu_xen->pv_time); + if (pv_info) + kvm_xen_update_vcpu_time(v, pv_info); + + srcu_read_unlock(&v->kvm->srcu, idx); } static int vcpu_attr_loc(struct kvm_vcpu *vcpu, u16 type,
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